Geochemical assessment of gold mine tailings proposed for marine tailings disposal

A preliminary geochemical study on gold mine tailings proposed for marine tailings disposal has been undertaken to identify the potential release of acidity and ecotoxic elements. Laboratory tests investigated the effects of flushing media, temperatures and light-exposure on the reactivity and acid generation potential of the tailing. Based on low sulphide and carbonate concentrations, ambiguous static test results categorized the tailing as 'uncertain to potential-acid-generating'. Over a 20-week kinetic test programme, tailing leachates remained circum-neutral and metal release rates decreased substantially after the first-flush. However, Canadian Interim Quality guidelines for marine sediment were exceeded for As, Cd, Cr, Cu, Pb and Zn by factors ranging between 1.5 (Zn) and 196 (As) and kinetic leachate concentrations of Cd exceeded Canadian Marine Aquatic Life guidelines suggesting potentially harmful effects might occur upon disposal of the tailing in marine environment. Leaching of ecotoxic elements was enhanced by the use of seawater as flushing medium. Changes in temperature and light exposure had only minor effects. In-situ long-term (> 20 weeks) leaching tests are proposed.